Recovery of deashed oil and naphthenic acids from residuum stocks



June 1952 E. M. HONEYCUTT RECOVERY OF DEASHED OIL AND NAPHTHENIC ACIDS FROM RESIDUUM sTocxs Filed Feb. 18, 1950 INVENTOR. EARL M. HONEYCUTT 22 E86 vm mm Q .23 2 5 2 =0 hm v2.8-3

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ATTORNEYS Patented June 17, 1952 RECOVERY OF DEASHED OIL AND NAPH- THENIC ACIDS FROM RESIDUUM STOCKS Earl M. Honeycutt, Claymont, Del., assignor to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey Application February 18, 1950, Serial No. 144,917

15 Claims. 1

This invention relates to the treatment of oil containing alkali metal naphthenates for the purpose of producing de-ashed oil and purified naphthenic acids or naphthenates. The invention is especially useful in the treatment of heavy residuum stocks containing asphaltic components.

In the refining of crude petroleum a commonly used procedure comprises subjecting the crude to a topping operation in which lower boiling fractions such as gasoline, kerosene and gas oil are distilled off, treating the reduced crude with an alkali such as caustic soda and then subjecting it to further distillation under vacuum to obtain the lubricating oil fractions. During the alkali treatin step acidic components such as naphthenic acids are converted into the form of alkali metal salts which, during the subsequent vacuum distillation, do not distill but remain in the residuum along with the asphaltic components and high boiling lubricating oil. The residuum stock thus obtained accordingly has a high ash or inorganic content due to thepres ence of the alkali metal naphthenates. For instance, in the practice of a process of this type such as described in Pew Patent No. 1,761,153, it has'been found that crudes of the naphthenic base type will yield a residuum generally containing about -9% by volume of naphthenic acids in the form of alkali salts or soaps and having an ash content of the order of 2-3%.

In order to render such residuum stocks suitable for use as fuel oil it is generally necessary to'reduce the ash content considerably. For a satisfactory commercial product it is desirable that the ash content be below 0.3% at most and preferably below 0.1%. It is also desirable to recover the naphthenic acids from the resid uum, as they have numerous special uses commercially. Particularly is it advantageous if the naphthenic acids can be recovered in a highly purified form, for example, containing less than 5% hydrocarbon oil, inasmuch as such products are especially valuable and command a* high price on the market.

One method of recovering naphthenic acids from residuum oil comprises treating the oil with strong sulfuric acid in sufficient amount to convert substantially all of the naphthenates into the acid form and then vacuum distilling the treated oil to remove the naphthenic acids. Such a process has been described in Terrell et a1. Patent No. 2,056,913. This type of process has the disadvantage that the inorganic salt resulting from acidification of the naphthenates remains in the asphaltic oil obtained from the distillation step, so that it is not rendered suitable for use as fuel oil, and that the naphthenic acids.

are obtained in impure form as a mixture containing large amounts of hydrocarbon oil. It has the further disadvantage that only a portiongenerally a minor portion-of the liberated naphthenic acids can be distilled from the acidified residuum under commercial operating conditions, which results in a considerable lossof valuable naphthenic acids.

Various other methods have been proposed for removing naphthenates from residuum oils which depend upon the preferential solubility of the naphthenates in water or certain aqueous organic solvents. These methods heretofore have not been entirely satisfactory due to the high emulsion-forming tendency of residuum oil and the high solubility of hydrocarbon components in the naphthenate-containing extract phase. posed do not appear to have been carried out under conditions such as to yield an oil product of suitably low ash content for fuel oil purposes while at the same time producing highly purified naphthenic acids.

The present invention is directed to and provides an extraction process which is capable of yielding both residuum oil of low ash content and naphthenic acids of highly pure quality. The efficiency of the process depends upon conducting the extraction in a particular manner under special conditions as hereinafter more fully described. While the process may be utilized in treating various charge oils containing,

solvent and containing at most only a very small amount of naphthenates. The oil phase is subjected to a vaporization step to remove solvent and yield de-ashed oil. The alcohol phase is countercurrently treated with fresh hydrocarbon solvent to remove the residual 011, after which The extraction methods heretofore prothe treated alcohol phase may be acidified to convert the naphthenates into naphthenic acids. The acidified mixture is settled to obtain a naphthenic acid phase containing hydrocarbon solvent and an aqueous alcohol phase containing salt in solution. Solvent is vaporized from the naphthenic acid phase to yield naphthenic acids, while alcohol is distilled from the alcohol phase to recover the same and yield salt water as bottoms.

In a more specific embodiment the hydrocarbon solvent which is admixed with the charge oil is that which has been used in the aforesaid countercurrent treating step and which contains residual oil extracted from the alcohol phase. This feature of operation results in considerable saving in solvent requirements for satisfactorily conducting the process.

The invention is more fully illustrated with reference to the accompanying drawing which is a more or less schematic fiowsheet, with'certain portions shown in section, illustrating one manner of practicing the process. In describing the process the charge material will be considered to be a residuum oil obtained by distillation of reduced crude in the presence of caustic soda and containing say -9% naphthenic acids in the form of sodium *naphthenates.

' Referring to the drawing, hot charge oil may be obtained directly from a refinery distillation step and introduced while still hot (e. g. 300-700 F.) into the system through line Ill. The heat content of the charge may be utilized to vaporize solvent, as more 'fully'described hereinaftenby flowing the charge through a heat exchanger II, from which it then flows through line l2 to a mixer [3. A stream of an aqueous propyl alcohol is introduced through line [-4 into the charge and also a hydrocarbon solvent stream is added thereto through line [5, the mixture of these materials then passing through mixer l3 where intimate contact'i's effected and thence into separator tank 15. The mixture in tank It readily separates, if proper conditions are maintained, into an upper oil layer containing most of the hydrocarbon solvent and atmost only a very small amount of naphthenate and a lower alcohol-layer containing thenaphthenates together with some residual oil and hydrocarbon solvent.

In order to produce from'the charge an oil product having a desirably low ash content several factors are especially important. In the first place the alcohol introduced through line 14 should be a propyl alcohol-either isopropyl or n-propyl-having a concentration of at least 20% byweight in water. Emulsion troubles are encountered if lower concentrations of the alcohol are employed. Secondly, the amount of aqueous alcohol added through line [4 should be sufficient to dissolve practically allof the-sodium naphthenates present in the charge oil. The minimum amount will vary considerably with the particular charge stock being treated. For example, when the charge contains about 5% naphthenic acids inthe form of naphthenates, the ratio of aqueous alcohol to charge on a volume basis should exceed 0.75; whereas when the naphthenic acid content is about 8%, such ratio should exceed 1.20. Generally little if any benefit will be derived in the treatment of residium by exceeding a ratio of 1.50 and the cost of recovering the alcohol will be proportionately increased.

Anotherfactor affecting the efficiency of separation in separator tank 16 is the amount of hydrocarbon solvent introduced through line I5.

It is important that the solvent be added in amount at least equal to the charge and it is preferable that the ratio of solvent to charge exceed 1.25. A proportion within the range of 1.40-1.75 is usually entirely satisfactory for conducting the operation and little if any advantage results from using larger proportions. If the amount of solvent introduced through line 15 is too low, the oil and alcohol phases will not separate from each other properly in tank 16 and consequently sodium naphthenates will remain in the oil layer and cause the oil product to have an undesirably high ash content.

The temperature for the settling step in tank lfishould be at least above F. and preferably should be above F. to insure an efficient separation. As a general rule the separation will be entirely satisfactory at temperatures of the order of -155 F. and the oil product will have an ash content of less than 0.1%. Still higher temperatures may be used, if desired, provided sufficient pressure is maintained to prevent boiling within tank 16. the use of pressure, it is desirable to maintain the temperature below 200 F. and usually considerably below this value. The temperature of the mixture passing from mixer l3 'to' tank [6 conveniently may be maintained at the desired value by properly regulating the heat transfer operation in exchanger I l From separator tank 15 the oil layer is withdrawn continuously adjacent the top through line 11 whence it'passes'through heat exchanger 1 l in indirect heat exchange with the charge and then into vaporizer 58. By transferring sufficient heat to the oil layer stream during its passage through exchanger II most of the hydrocarbon solvent contained therein may be flashed mi in the upper part of vaporizer 58. Any minor portion of solvent remaining is stripped from the oil by means of steam which is introduced into the lower part of the vaporizer through line 59. Solvent-free oil of low ash content is Withdrawn from the bottom of the vaporizer by means of line I8 as one product of the process.

The alcohol layer which settles to the bottom of tank It generally contains residualoil to the extent of about 20% on a solvent-free basis. A stream of the alcohol layer is continuously withdrawn through line I!) and sent through line22 and cooler 23 into countercurrent extraction column 20 for removing residual oil. If it is desired also to remove phenolic compounds so that the naphthenic acid product will bephenol-free, this may be done by injecting through line '24 and valve 25 a small amount'of mineral acid, such as sulfuric acid, suflicient to preferentially neutralize the phenolates along with only a small amount of naphthenates of relatively high molecular weight. Any phenolic compounds and naphthenic acids thus liberated by the mineral bon solvent used for this purpose should be a saturate hydrocarbon or mixture of hydrocarbons having 5-10 carbon atoms per molecule. Unsat urated hydrocarbons such as aromatics and ole- However, in order to avoid fins should not be present to any substantial extent in the solvent for the reason that they tend to decrease the extraction efficiency considerably, possibly due to their relatively high solubility in the aqueous alcohol .used in the process. It is also preferred, although not mandatory, that the solvent contain little if any naphthene hydrocarbons, as compounds of this type tend to cause flooding in the extraction column and necessitate lower extraction rates. Accordingly, it is preferred to use a hydrocarbon solvent which is composed substantially completely of paraflinic hydrocarbons within the specified range. It is still more preferable, when operating the process in the manner illustrated in the accompanying drawing, to employ a solvent composed mainly of Ca paraflinic hydrocarbons for economic reasons relating to recovery of the alcohol and hydrocarbon solvent as more fully explained hereinafter. For example, an alkylate fraction composed mainly or essentially of Ce isoparaflins is an espe cially suitable solvent for use in the process.

For satisfactorily conducting the countercurrent extraction to produce naphthenic acids of suitably low oil content, it has been found that the aqueous propyl alcohol used in the process should have an alcohol content not exceeding about 40% by weight. Higher alcohol contents result in too high oil-solubility in the alcohol phase. Thus the concentration of alcohol should be within the range of 20-40%. Best over-all results are obtained by using aqueous alcohol of about 25%, for instance 24-26% alcohol.

For best results the temperature employed in the countercurrent treatment in column 20 should be within the range IOU-130 F. It has been found that temperatures either below or above these values may tend to cause flooding within the column and require lower extraction rates. Since the temperature in tank ['6 generally will be maintained somewhat higher than desired in the countercurrent treating step, cooler 23 may be provided in line 22 for cooling the alcohol layer stream before it enters column 20. Preferably the countercurrent extraction is carried out at a temperature in the neighborhood of 115 F.

The hydrocarbon solvent stream issuing from the top of column 20 will contain residual oil extracted from the alcohol layer along with any phenolic compounds and naphthenic acids which have been liberated in case mineral acid was introduced through line 24. The withdrawn mixture preferably is sent through line [5 for introduction into the incoming charge. This feature of using solvent successively in the countercurrent treating step and then in the charge treating step considerably reduces the over-all solvent requirements as compared to operating with fresh hydrocarbon solvent for each step.

The oil content of the treated alcohol layer issuing from the bottom of column 20 will depend upon the amount of hydrocarbon solvent used for the extraction and the number of transfer stages provided by the column as well as upon the concentration of alcohol used. It has been found that by employing hydrocarbon solvent of the type specified in volume amount at least equal to the charge oil and using aqueous alcohol of 20-40% concentration, a naphthenic acid product of very low oil content, for example, 5% or less, may readily be obtained with a feasible number of theoretical extraction stages in the extraction column.

The treated alcohol layer passes from the bottom of column 20 through line 33. In order to line 40.

convert the naphthenates into naphthenic acids a mineral acid is introduced through line 34 in substantially stoichiometric amount. Any strong mineral. acid, such as sulfuric acid, may be used for this purpose and the concentration of'acid used has no special significance. The acidified mixture then passes through line 35 into settling tank 36 where a separation of layers is obtained. The naphthenic acid phase containing some hydrocarbon solvent rises to the top and the aqueous alcohol containing inorganic salt resulting from the neutralization settles to the bottom. The presence of hydrocarbon solvent in the naphthenic acid layer is advantageous in that it reduces its viscosity and facilitates the separation. It should also be. noted that the use in the process of relatively dilute propyl alcohol as previously specified is advantageous in that it permits the inorganic salt formed from neutralization of the naphthenates to remain in solution in the aqueous alcohol layer obtained in tank 36.

The upper layer from tank 36 is withdrawn through line 3'! and passed to heater 38 which is adapted to supply sufiicient heat for flashing off most of the contained hydrocarbon solvent. The heated mixture then flows into vaporizer 39 where flash vaporization of the solvent occurs. The small amount of solvent remaining in the naphthenic acids is stripped therefrom by introducing steam into the lower part of the vaporizer through Purified naphthenic acids are removed from the bottom of the vaporizer by means of lin 4| as another product of the process.

The remainder of the process concerns the recovery of the alcohol and hydrocarbon solvent for re-use. It has been found that the use of a Ca hydrocarbon or mixture of hydrocarbons as the hydrocarbon solvent permits the recovery to be effected in a particularly satisfactory and efficient manner. The salt-containing aqueous alcohol layer from the bottom of tank 35 is sent through line 42 to a distillation column 43 wherein it is introduced near the top. Hydrocarbon solvent vapors and steam from vaporizer 58 are passed through line 44 into the lower part of column 43, While solvent vapors and steam from vaporizer 39 flow through line 45 also into the lower part of the distillation zone. By operating in this manner the heat contained in the vapors introduced into the bottom of column 43 may be utilized to effect recovery of aqueous alcohol for re-use. The aqueous alcohol is obtained as distillate from the column along with a portion of the hydrocarbon solvent which also passes overhead. The mixture of alcohol, water and hydrocarbon vapors is sent through line 46 to condenser 41 and the condensate then flows through line 48 to separation tank 49. The degree of fractionation in column 43 may, if desired, be controlled so that the alcohol thus recovered has the proper concentration for re-use, namely 20-40% by weight in water and preferably about 25%. However, it is generally more economic from the standpoint of heat requirements to distill off the alcohol in a concentration in equilibrium with the composition of feed introduced through line 42. The proportion of water to alcohol at such concentration will be considerably lower than is required for re-use of the recovered alcohol; accordingly, make-up water may be added through line 56 and valve 51 in such amount that the recovered alcohol in separation tank 49 has the desired concentration within the range of 20-40%.

From the bottom of the distillation column a mixture of salt Water and hydrocarbon solvent is transferred via line 50 e to separation tank :l wherein the hydrocarbon-solvent rises to. the top andxsalt water settles to the bottom. The separated hydrocarbon solvent passes through line. 52 to. tank for-re-use. Salt water. is removed from the systemby means of line 53.at. thebottom of tank 551. The amount of'water thus removed from the .process should .be equivalent to :the amount of water added. in the form ofstea-mto Vaporizers-58 and 39 and as make-up from line 56.

From. the top of tank lfl'hydrocarbon solvent is recycled by-means of lines'54 and'32 to thecountercurrent extraction zone, while aqueousalcohol is-returned from the bottom by means of lines 55iand M. for re-use mtreating the charge.

The following specific example illustrates" the use of preferred conditions in practicing :the process:

They charge. stock is a heavy residuum obtained from vacuum distillation of a-causticsodaztreated reduced crud-ederived from naphthenic base petroleum and having approximately the following properties:

A. P. I. gravity=ll Furol viscosity at 210 F.=320

Ash content=2.5

Naphthenate content (as vol.

acids) =G% I The. charge stock is mixed with'l.25 times its volume of aqueous isopropanol of 25% concentration and with 1.5 times its volume of C8 alkylate which has been used for countercurrent treatment of the naphthenate-containing alcohol layer. The mixture is settled at a temperature of 150 F. to'separate the oil phase from the alcohol phase. Solvent is removed from the oil phase by vaporization and steam stripping, and oil having anash content ofabout 0.06% is thereby obtained. The alcohol layer is countercurrently treated at a temperature of 115 F. with fresh Cs alkylate in anextraction column having about 7 theoretical stages. The treated alcohol layer is acidified with sulfuric acid having a conm naphthenic tration of 45% H2804 and thensettled to obtain a-naphthenic acid layer-and a salt-containing alcohol. layer. Upon vaporizing solvent from the naphthenic acid layer and'steam stripping, .a purifiednaphthenic acid product is obtained-Which contains 2.6% oil by weight. Aqueousalcohol of about 25% concentration is-recovered from the lastamentioned. alcohol layer bydistillation and salt- Water remaining as bottoms is discarded.

The particular extraction procedure employed in ..the above described process may ,be. used in treating any oil .Which contains alkali metal naphthenates but is especially important where the charge oilis anv asphaltic residuum. The steps ofifirst mixingthe charge with the-specified solvents, separating 01f the oil layer and then countercurrently extracting only the .alcohol layer avoids many .of the diilicultiesusually encountered in extracting residual oils. Under the conditions specified the first settling step 'eifects a nearly complete separation of naphthenates from the oilso that a :fuel oil product having less than 0.1% ash content may readily be obtained. Furthermore, generally about. 98% of .the oil and asphaltic components present in the charge are removed at this point, thusgreatly improving the eifectiveness of the subsequent .countercurrent extraction step. Theresidual oilicontained in the alcohol layer-introduced .to the countercurrent extractionmay readily .be reduced in-the countercurrent treatmentto :a .very low value under. operating conditions .which are entirely feasible for plant practice.

'5 It will be apparent that modifications. of i the process maybe made without departing from the. scope of the invention. For-example, fresh hydrocarbon solvent may be used in. thecharge extractionstep inplace of: the oil-.cOntainingsOI- ventstream-fed from thetop ofcolumnmphowever, ;.as previously mentioned, practice of the process in the manner. described 'e'fiects considerableeconomies of operation. .Also, if desired, purified;-naphthenate salts may be obtaineddirectly from the countercurrently'treated alcohol layer .by 1 evaporation of the contained solvents, thus dispensing-with the acidification .by. means of mineral acid.

.Havingxdescribed my invention, what .I .claim a-nddesire to protectby Letters Patent is:

1.1 Method ofproducing de-ashed oiland purified. naphthemc acids from a residuum, charge oil containing alkali metal.naphthenates'which comprises intimately admixing the charge oil with an aqueous propyl alcohol .containing 20-40% by weight .of the alcohol in sufilcient amount to. dissolve at least most of the naphthenates and with at least an equal volume amount of a hydrocarbon solvent composed essentially of saturate hydrocarbon within the (35 010 range, settling the mixture at-a temperature above F. to separate analcohol phase from an oil phase, vaporizing solvent from the oil phase to yield 'de-ashed oil, countercurrently treating the alcohol phase with hydrocarbonsolvent composed as previously specified to remove residual oil, acidifying the countercurrently treatedalcohol phase, settling the acidified mixture toseparate a naphthenic acid phase containing hydrocarbon solvent from an aqueous alcohol phase containing salt, vaporizing'solvent from said naphthenic acid phase to obtain purifled naphthenic acids and distilling alcohol from the last-mentioned alcohol phase to recover the sameand yield salt wateras bottoms.

2. Method of producing de-ashed oil and purified naphthenic acids from aresiduum charge oil containing-alkali metal naphthenateswhi'ch'comprises intimately admixing thecharge oil'with an aqueous propyl alcohol containing -20+40% by weight of the alcohol in sufilcient amount to dissolve at least most of the naphthena-tes-and withat least an equal volume amount ofa hydrocarbon solvent composed essentially ofparaffinic hydrocarbon within the Cs-Om range, settling the mixture at a temperature within the-range of 80-200 F. to separate-an alcohol phase from an oilphase, vaporizing solvent from the-oil phase to yield de-ashed oil, countercurrentlytreating the alcohol phase with hydrocarbon solvent-composed as previouslyspecifiedto remove residual oil, acidifying the countercurrently treated alcohol phase, settling the acidified mixture to separatea naphthenic acid phase containing hydrocarbonsolvent from an aqueous alcohol phase containing salt, vaporizing solvent from said naphthenic acid phase to obtain purified naphthenic acids and distilling alcohol from the lastmentioned alcohol phase to recover the sameand yield saltwater as bottoms.

'3. Method :according to claim 2 wherein-the hydrocarbon solvent is-mainly Cs paraffinic hydrocarbon, the temperature of said countercurrcnttreatment is =130 F. and the alcoholin said aqueous propyl alcohol is isopropyl in a concentration of about 25% by weight.

-.4...Method according to claim 2:.wherein the volume amount of hydrocarbon solvent used is at least 1.25 times the amoun of charge oil and the temperature in the first-mentioned settling step is at least 125 F.

5. Methodaccording to claim 4 wherein the hydrocarbon solvent is mainly Cs parafiinic hydrocarbon, the temperature of said countercurrent treatment is IOU-130 F. and the alcohol in said aqueous propyl alcohol is isopropyl in a concentration of about 25% by weight.

6. Continuous method -or producing de-ashed oil and purified naphthenic acids from a residuum charge oil containing alkali metal naphthenates which comprises intimately admixing the charge oil with an aqueous propyl alcohol containing 20 40% by weight of the alcohol in sufiicient amount to dissolve at least most of the naphthenates and with the hereinafter specified hydrocarbon solvent stream, settling the mixture at a temperature above 80 F. to separate an alcohol phase from an oil phase, vaporizing solvent from the oil phase to yield de-ashed oil, countercurrently treating the alcohol phase with a hydrocarbon solvent composed essentially of saturate hydrocarbon within the C5C10 range to remove residual oil, said solvent being used in amount by volume at least equal to the charge oil, introducing the solution of oil in solvent resulting from said countercurrent treatment to the charge oil as the said specified hydrocarbon solvent stream, acidifying the countercurrently treated alcohol phase, settling the acidified mixture to separate a naphthenic acid phase containing hydrocarbon solvent from an aqueous alcohol phase containing salt, vaporizing solvent from said naphthenic acid phase to obtain purified naphthenic acids and distilling alcohol from the last-mentioned alcohol phase to recover the same and yield salt water as bottoms.

7. Continuous method of producing de-ashed oil and purified naphthenic acids from a residuum charge oil containing alkali metal naphthenates which comprises intimately admixing the charge oil with an aqueous propyl alcohol containing 20-40% by weight of the alcohol in suificient amount to dissolve at least most of the naphthenates and with the hereinafter specified hydrocarbon solvent stream, settling the mixture at a temperature within the range of 80-200 F. to separate an alcohol phase from an oil phase, vaporizing solvent from the oil phase to yield deashed oil, countercurrently treating the alcohol phase with a hydrocarbon solvent composed essentially of parafiinic hydrocarbon within the C5-C1o range to remove residual oil, said solvent being used in amount by volume at least equal to the charge oil, introducing the solution of oil in solvent resulting from said countercurrent treatment to the charge oil as the said specified hydrocarbon solvent stream, acidifying the countercurrently treated alcohol phase, settling the acidified mixture to separate a naphthenic acid phase containing hydrocarbon solvent from an aqueous alcohol phase containing salt, vaporizing solvent from said naphthenic acid phase to obtain purified naphthenic acids and distilling alcohol from the last-mentioned alcohol phase to recover the same and yield salt water as bottoms.

8. Method according to claim '7 wherein the hydrocarbon solvent is mainly Cs paraffinic hydrocarbon, the temperature of said countercurrent treatment is 100-130" F. and the alcohol in said aqueous propyl alcohol is isopropyl in a concentration of about 25% by weight.

"9. Method according'to claim {wherein the volumeamount of hydrocarbon solvent used is hydrocarbon solvent is mainly'Cs' paraflinic hydrocarbon, the temperature of said countercurrent treatment is 100-130 F. and the alcohol'in said aqueous propyl alcohol is isopropyl in a concentration of about 25% by weight of the alcohol.

11. In a continuous process for treating a residuum oil charge containing alkali metal naphthenates to produce de-ashed oil and to purify and naphthenates, the steps which comprise intimately admixing the charge oil with an aqueous propyl alcohol containing 20-40% by weight of the alcohol in sufiicient amount to dissolve at least most of the naphthenates and with the hereinafter specified hydrocarbon solvent stream, settling the mixture at a temperature above F. to separate an alcohol phase from an oil phase, countercurrently treating the alcohol phase with a hydrocarbon solvent composed essentially of saturate hydrocarbon within the Cs-Cio range to remove residual oil, said solvent being used in amount by volume at least equal to the charge oil, and introducing the solution of oil in solvent resulting from said countercurrent treatment to the charge oil as the said specified hydrocarbon solvent stream.

12. Process according to claim 11 wherein the volume amount of hydrocarbon solvent used is 1.25-1.75 times the amount of charge oil, the temperature in the settling step is 125-200 F. and the temperature in the countercurrent treating step is -l30 F.

13. Process according to claim 12 wherein the oil solvent is mainly C's paraifinic hydrocarbon.

14. Process according to claim 13 wherein the alcohol in said aqueous propyl alcohol is isopropyl in a concentration of about 25% by weight of the alcohol.

15. Continuous method of producing de-ashed oil and purified naphthenic acids from a residuum charge oil containing alkali metal naphthenates which comprises intimately admixing the charge oil with an aqueous propyl alcohol containing 20-40% by weight of the alcohol in sufficient amount to dissolve at least most of the naphthenates and with the hereinafter specified hydrocarbon solvent stream, settling the mixture at a temperature above 80 F. to separate an alcohol phase from an oil phase, stripping solvent from the oil phase by means of steam to yield de-ashed oil, countercurrently treating the alcohol phase with a saturate hydrocarbon solvent composed mainly of Ce parafiinic hydrocarbon to remove residual oil, said solvent being used in amount by volume at least equal to the charge oil, introducing the solution of oil in solvent resulting from said countercurrent treatment to the charge oil as the said specified hydrocarbon solvent stream, acidifying the countercurrently treated alcohol phase, settling the acidified mixture to separate a naphthenic acid phase containing hydrocarbon solvent from an aqueous alcohol phase containing salt, stripping solvent from said naphthenic acid phase by means of steam to obtan purified naphthenic acids, introducing the last-mentioned alcohol phase into a distillation zone, introducing vapors from each of said stripping steps into said distillation zone below the locus of introduction 11 12 of the alcohol phase. distilling aqueous alcohol REFERENCES CITED and a portion of the hydrocarbon solvent over- The fo-nowmg references are of record {in the head by means of heat contained in theintrofil of this patent:

duced vapor, condensing the overhead -vapors and settling the condensate to separate aqu- 5 UNITED STATES PATENTS eous alcohol from hydroearbon solvent. and Number Name Date settling the bottoms product from the distilla- 1,712,475 Buc May '2, 1929 tion to separate salt water .irom the other por- 2,069,172 Miller Jan. 26, 1937 tion of hydrocarbon solvent. 2,510,806 Egberts et a1. June 6, 1950 10 EARL M. HONEYCU'I'I'. FOREIGN PATENTS Number Country Date 323,784 Great Britain Jan. 10, 1930 

1. METHOD OF PRODUCING DE-ASHED OIL AND PURIFIED NAPHTHENIC ACIDS FROM A RESIDUUM CHARGE OIL CONTAINING ALKALI METAL NAPHTHENATES WHICH COMPRISES INTIMATELY ADMIXING THE CHARGE OIL WITH AN AQUEOUS PROPYL ALCOHOL CONTAINING 20-40% BY WEIGHT OF THE ALCOHOL IN SUFFICIENT AMOUNT TO DISSOLVE AT LEAST MOST OF THE NAPHTHENATES AND WITH AT LEAST AN EQUAL VOLUME AMOUNT OF A HYDROCARBON SOLVENT COMPOSED ESSENTIALLY OF SATURATE HYDROCARBON WITHIN THE C5-C10 RANGE, SETTLING THE MIXTURE AT A TEMPERATURE ABOVE 80* F. TO SEPARATE AN ALCOHOL PHASE FROM AN OIL PHASE, VAPORIZING SOLVENT FROM THE OIL PHASE TO YIELD DE-ASHED OIL, COUNTERCURRENTLY TREATING THE ALCOHOL PHASE WITH HYDROCARBON SOLVENT COMPOSED AS PREVIOUSLY SPECIFIED TO REMOVE RESIDUAL OIL, ACIDIFYING THE COUNTERCURRENTLY TREATED ALCOHOL PHASE, SETTLING THE ACIDIFIED MIXTURE TO SEPARATE A NAPHTHENIC ACID PHASE CONTAINING HYDROCARBON SOLVENT FROM AN AQUEOUS ALCOHOL PHASE CONTAINING SALT, VAPORIZING SOLVENT FROM SAID NAPHTHENIC ACID PHASE TO OBTAIN PURIFIED NAPHTHENIC ACIDS AND DISTILLING ALCOHOL FROM THE LAST-MENTIONED ALCOHOL PHASE TO RECOVER THE SAME AND YIELD SALT WATER AS BOTTOMS. 